19 January 2019

Windows 10 1803 failed update week-long nightmare

In December 2018 I bought a laptop with Win10 (Asus, for the records, but I think it doesn't matter). It has been little responsive since the beginning, so I let it run all updates for 24 hours: at least it stopped using the hard-disk like crazy.

But it still complained that there were pending updates, the "Windows 10 1803", that had already failed three times to install. I don't know which version was running, probably it had arrived to 1709 (that is Fall 2017).

Microsoft forums already gave the workaround: skip the 1803 update and go for 1809. Alright, but how? As of January 2019, Microsoft-provided tools would not do it.

After a week of wasted evenings I was successful with:
  1. downloading the [correct] 1809 ISO from the the Microsoft downloads site pretending not-to-be a Microsoft browser (do it from Linux or use the documented trick for Internet Explorer/Edge); it is a circa 5 GB file
  2. burning the ISO into an USB pendrive (min 8 GB) with Rufus tool under Windows
  3. going into the laptop BIOS and disabled Secure Boot
  4. from the BIOS forced to boot from the USB pendrive
  5. installed the update by choosing to keep existing files
Step #5 took few hours (overnight) and my files were not lost. Do yourself a favour and backup first, just in case!

I dare to say it is not for the unexperienced user; friends confirmed that there is no Microsoft-ish way out if 1803 update doesn't install: it would go on forever killing your HDD, CPU and Internet bandwidth.

Tip. If you want to control when Win10 downloads and installs updates, find the way to mark your connection as metered.

Good luck.

05 January 2019

Taking control of HP 9403A

The HP 9403A odyssey might be close to an end. After tracing most connections on the "DVS Program I/O" connector to corresponding ICs, thus understanding if they are inputs or outputs (they all end up into an HP 1820-0107 level adapter), I begun to take control of the device:

HP 9403A: first signs of human control after 40 years.
I know which are control lines and which are data lines. There is no serial protocol, but just plain parallel negative logic. If I want to do something with the bulky piece of equipment I will need a microcontroller with lots of I/O lines, or some serial-to-parallel (open collector) converter.

02 January 2019

HP 1820-0107 pinout

I have finally found some documentation about HP 1820-0107 custom IC from 1970's. It is (hidden) in the HP 3720A manual.
HP 1820-0107 as documented in HP 3720A manual.

That document describes it as "Interface buffer gate" and draws the chip pinout as follows:
Well, I've never seen a NOT gate with two inputs. I confirm Vin is a Vcc pin (+5V in my case). In a custom chip Vout could make sense, but why so close to the Vin pin?!

In the next page of the same document I see this:

which makes more sense considering two Voltage pins and the NOT symbol. Further down the manual, the schematic diagram the corresponding ICs (A6MC21, 25, 31, 33, 35) are drawn as interface inverting gates:

Alright, now this makes sense! It explains the presence of resistors on data lines in various places of the HP 9403A. But, most important:
  1. the 1820-0107 is not a flip-flop of any sort (easier to reverse engineer the circuit)
  2. the input pin requires pulling down to ground (which explains why I haven't found yet a common +V line on connectors towards the external world)
 Back to the PCBs now!